This invention relates to a lubricating oil filter assembly of the type used on internal combustion engines. More specifically, the invention relates to a filter assembly having a spin-on or throwaway type filter cartridge adapted to be secured to a mounting adaptor on an engine having two lubricating oil circuits.
Early prior art generally utilized a separate filter assembly for each lubricating oil circuit of the engine. Succeeding art combined two filter elements into one filter assembly in order to reduce maintenance, service and inventory. Filter assemblies of this type are disclosed in Offer U.S. Pat. No. 3,586,171 and Brown U.S. Pat. No. 4,738,776.
The Offer patent discloses a spin-on filter with two filter elements in an axially stacked arrangement. One of the filter elements is a relatively short section having a coarse filter medium which is commonly referred to as a depth-type media. The other filter element is longer and utilizes a finer filter medium which is the typical pleated paper or surface-type media. The shorter, coarser filter element is closest to the inlet/outlet positions on the mounting adaptor while the longer, fine-media filter element is positioned at the farther end of the spin-on cartridge. A cylindrical hollow stem is located in the center of the outlet opening of the adaptor and is sealably engaged by a rubber seal on the longer filter element. This separates the flow of lubricating oil to the two circuits.
The Brown patent also discloses a filter assembly with two distinct filter elements arranged as a stack, one on top of the other. In this case, however, the shorter of the two elements contains the finer filter medium which is defined by a plurality of stacked disks. The longer section contains a coarser filter medium which is formed by a pleated paper arrangement. This section is located closer to the inlet/outlet positions on the mounting adaptor. Separation of oil flow from the two sections is established by a cylindrical, hollow core located in the longer section. The core provides a seal where the two sections abut and, at the opposite end of the longer section, a rubber seal suitably communicates with the core. The seal also communicates with and engages a protuberance of the mounting adaptor in order to effect separation of lubricating oil flow for the two oil circuits.
While combined filter assemblies of the type disclosed in the Offer and Brown patents reduce service and inventory requirements, sacrifices have been made in many areas. A combined filter assembly is more complex and costly than an individual filter assembly with one filter element and one oil flow path. The combined filter must function in an environment serving two oil circuits operating at independent and usually different pressures with a resulting difference in the pressure differential. The structure required for separation of the circuits accounts for the complexity and a major portion of the added cost.
The size of the combined filter assembly often is approximately the same as that of an individual assembly. The manufacturer must provide for additional contaminant capacity in the combined filter in order to avoid a sacrifice in service life or change interval.